Im a very frequent gunship-starter, I usually opt for them as long as the map isnt completely flat or too small. Alot of the value is intangibles like your opponent having less experience dealing with a gunship start than a rover start, or triggering an overreaction of AA.
Alot of the options have razor-thin timeframes of utility. A single harpy + radar can do all your anti-raider till about the 4 minute mark when mobile AA shows up. Blastwings get one free shot before picket+radar, best used after your opponent has done their initial econ.
Now at about the 5-6 minute mark you better have a land factory, if you spent metal on anything else you're probably dead by now. If you can pull off the transition then you're in a good spot, very early game and you have the options of a air+land fac already.
The big downsides are their vulnerability and speed.
- Constructor costs 300, but gains little advantage by being a flyer as fleas can still target it.
- Once they start taking damage, gunships often arent fast enough to disengage before dying
- Bad value. If you wanna go out destroying some mexes and llts you might be looking at around 1000 metal for 5 locusts or 760 for a nimbus.
- Lack sticking power. Glaives and ronins can dance around and tie enemy units up at the point of engagement, preventing them from going somewhere else, gunships dont really have this so your opponent can go where they please.
In conclusion, I think the dirtbag should be added to the gunship tree.